Secure data transmission in optical networks is one of the hottest topics today. Surprisingly, quite a few real solutions have been proposed which would prevent intrusion to the optical networks and/or prevent interception of information by intruders.
For example, US 2004037556AA describes systems and methods for actively monitoring and managing the integrity of an optical fiber communications link. The optical fiber link integrity is monitored to guard against intrusions and other security breaches. In one embodiment, a local and a remote active monitoring system are coupled by four fiber paths that provide primary and back-up transmit and receive paths between communication equipment. In one embodiment, a security light signal is transmitted using a secondary wavelength that differs from the wavelength used to transmit a user data light signal and travels in an opposite direction relative to the user data light signal. An active monitoring system monitors both administrative information contained within the security light signal and the intensity of the security light signal to manage the integrity of the fiber optic link. Methods are provided to characterize events impacting the fiber optic link integrity.
The above technology only provides monitoring of the fiber integrity.
A problem of possible interception of data by an intruder and a problem of securing the data are not even discussed.
Another approach utilizes a polarization detector. US2006153491AA describes an intrusion detection system for use on single mode optical fiber, using a polarimeter. In the US2006153491AA, a telecommunications optical fiber is secured against intrusion by detecting manipulation of the optical fiber prior to an intrusion event. This can be used in a non-locating system where the detection end is opposite to the transmit end, or in a locating system which uses Fresnel reflections and Rayleigh backscattering to the transmit end to detect and then locate the motion. The Rayleigh backscattering time sliced data can be stored in a register until an intrusion event is detected. The detection is carried out by a polarization detection system which includes an optical splitter which is manufactured in simplified form for economic construction. This uses a non-calibrated splitter and less than all four of the Stokes parameters. It can use a polarimeter type function limited to linear and circular polarization or two linear polarizers at 90 degrees.
The above solution also deals with detecting cases of rude physical intrusion into the optical transmission line and does not discuss a problem of securing data in cases when optical fibers are not damaged.
U.S. Pat. No. 4,847,831A describes a bidirectional repeater for Manchester encoded data (MED) signals present on a coaxial cable and fiber optic cable forming the transmission media of a local area network. The repeater receives and then reconstitutes the MED signals present on the coaxial cable and transmits the reconstituted MED signals onto the fiber optic cable. MED data present on the fiber optic cable is received, reconstituted, and transmitted onto the coaxial cable. Signals can be received from only one cable at any one time. Transmission of reconstituted MED signals is terminated when a special set of MED signals identifying the end of a transmission by a module of the network is received.
To the best of the Applicant's knowledge, most of the prior art solutions in the field deal with detecting a fiber cut/damage, while none of them propose a solution for preventing interception of a data signal, effective in cases when the interception is performed without cutting the optical fiber (i.e., in cases where the eavesdrop cannot be revealed by detecting a vulgar fiber cut).